A murderer and a violent criminal are being hunted after they absconded from an open prison.

Darren Douglas, 46, originally from Birmingham, and Ricardo Dunn, 32, previously of Burnley, Lancashire, absconded from HM Spring Hill open prison in Grendon Underwood, Buckinghamshire, in the early hours of Sunday.

Douglas was serving a life sentence for a murder he committed in Birmingham in 1998. He stabbed a man outside a pub.

Dunn was serving an indeterminate sentence following a conviction for GBH with intent in Burnley. He assaulted a man following a row in the street in 2009.

Chief inspector Olly Wright, of Thames Valley Police, said: "We are keen to speak to anyone who may have seen these men in the area and can provide us with information about their movements.

"These men were both convicted for violent offences and I would advise anyone who sees them, to not approach them and call police immediately.

"Both men have links with other areas so may have travelled out of the Thames Valley to those areas. I would like to remind people that it is a criminal offence to harbour these men and anyone caught doing so would be arrested."

The issue of prisoners walking out of open prisons has been in the spotlight since "Skullcracker" Michael Wheatley went on the run.

In May, the 55-year-old sparked a nationwide manhunt after he absconded from Category D jail HMP Standford Hill on the Isle of Sheppey, Kent.

The prolific armed robber - dubbed the "Skullcracker" for pistol-whipping innocent bystanders during raids - went on to rob a building society in Surrey.

He was already serving 13 life sentences for a string of raids when he disappeared, sparking a political row over the day release of dangerous criminals.

After being caught, he was sentenced at Guildford Crown Court to life behind bars and told he will serve at least 10 years before being eligible for parole.

It has also emerged that two prisoners, Scott Callaghan, 35, and Billy Harkins, 29, disappeared from the same prison on Saturday.

Callaghan is serving a sentence for perverting the course of justice and Harkins for aggravated burglary, Kent Police said.

Last month Sussex Police revealed that 89 prisoners had gone missing since the 1970s from Ford open prison and are still unaccounted for.